The objectives of these studies are to delineate the rapid regulation, primarily hormonal, of lipid and lipoprotein synthesis in rat liver and intestinal mucosa. Rat hepatocytes, isolated following perfusion of the liver with collagenase, will be used to measure the effects of cyclic nucleotides and hormones on the incorporation of tritiated water into cellular fatty acids and cholesterol. Similar studies will be carried out on intestinal mucosal cells dissociated by filling the intestinal lumen with various salt solutions as described by Weiser. Effects of fatty acids on lipid synthesis as well as fatty acid esterification and oxidation will also be studied in intestinal mucosal cells. Efforts will be continued to demonstrate phosphorylation of MHG CoA reductase in liver microsomes by a protein kinase and dephosphorylation of the enzyme by phosphoprotein phosphatase as an explanation of the inhibition of the enzyme by cyclic AMP and its activation by incubation of the 10,000 x g supernatant from liver. Radioimmunoassays for rat serum lipoproteins will be developed to measure the release of serum lipoproteins from rat hepatocytes and intestinal mucosal cells. Lipoprotein synthesis will also be measured by incorporation of labeled leucine into lipoprotein peptides, separated by immunoprecipitation, released from these cells into the incubation medium and remaining within the cells. The effects of hormones, fatty acids and drugs on lipoprotein synthesis and release will be investigated.